HIVE-26072: Enable vectorization for stats gathering (tablescan op).

[ayushtkn]

After https://issues.apache.org/jira/browse/HIVE-23530 , almost all compute stats functions are vectorizable. Only function that is not vectorizable is "compute_bit_vector" for ndv statistics computation. This causes "create table as select" and "insert overwrite select" queries to run in non-vectorized mode.

Even a very naive implementation of vectorized compute_bit_vector gives about 50% performance improvement on simple "insert overwrite select" queries. That is because entire mapper or reducer can run in vectorized mode.

[rbalamohan]

compute_bit_vector is vectorized via https://issues.apache.org/jira/browse/HIVE-24510

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[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Feel free to reach out on the [email protected] list if the patch is in need of reviews.